1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly, the present invention is best suited when applied to a semiconductor device using a resin insulating film such as polyimide, BCB, or the like.
2. Description of the Related Art
Conventionally, a resin insulating film such as polyamide, BCB, or the like is generally used as a front face protective film for a chip mounted by mold, etc.
An example of a chip using an insulating film such as polyamide, BCB, or the like as a front face protective film is shown in FIG. 8A to FIG. 8E. FIG. 8A and FIG. 8B are plan views showing a front face of the chip. FIG. 8C is a sectional view taken along the V—V line in FIG. 8B. FIG. 8D is a sectional view taken along the VI—VI line of FIG. 8B. FIG. 8E is a bottom view showing a reverse face of the chip.
On an operating layer of a semiconductor substrate 101, a source electrode, a gate electrode and a drain electrode are formed in a shape of teeth of a comb. A source pad 102, a gate pad 103 and a drain pad 104 are respectively led out from the respective electrodes on the front face of the semiconductor substrate 101.
The upper side of the operating layer of the semiconductor is covered with a surface protective insulating film 105, such as polyamide, etc. A view in FIG. 8A shows a specification in which only the upper side of the operating layer is covered with the surface protective insulating film 105. A view in FIG. 8B shows a specification in which all the regions except the respective pad areas 102 to 104 are covered with the surface protective insulating film 105. Thus, exposure of the electrodes and the semiconductor area on the front face of the chip is reduced so as to take a structure aiming for improvement of reliability.
Generally on the chip as structured above, the source pad 102 is connected to a pad 102A on the reverse face of the chip through a via hole 102B, and the pad 102A on the reverse face is mounted as ground of the source.
As described above, an insulating film such as polyamide, BCB, or the like is often used as a front face protective film of a conventional chip. However, a device using polyamide or BCB cannot be utilized for an application which requires a high reliability. For example, polyamide has a high water absorbing property and would be saturated with absorbed water in the long term. Then, the water would be soaked out up to fingers such as the gate, the source, and the like to induce corrosion, ion migration, and so on. Therefore, there could be a risk of causing a malfunction in the device. On the other hand, BCB has an extremely small water absorbing property. However, the interface between metal and BCB, and BCB itself would be permeated with water. Therefore, there could be a risk of causing the aforementioned trouble.
As a result of the above-described problems related to moisture resistance, a highly airtight hermetic seal package is used for a device which requires higher reliability. However, a hermetic seal package is extremely expensive and in some cases it costs several times as much as a chip.